In a negative differential resistance (NDR) device in contrast to typical resistance devices, the current decreases despite an increase in the voltage applied. That is, the current decreases as the voltage increases. Therefore, the voltage-current curve has an “N” shape, and, thus, the NDR device shows characteristics of diodes with various threshold voltages. Accordingly, the NDR device can be used to implement a multi-valued logic circuit which can display various logic states.
The NDR device is generally known as being observed in an Esaki diode, a resonant tunneling diode, a single electron transistor, a molecular device, and the like. In the Esaki diode which can be implemented with a heavily doped PN junction, when a voltage having a predetermined value or more is applied, a diffusion current mainly affects an operation of the Esaki diode, and, thus, a negative differential resistance characteristic with a peak and a valley can be observed. Meanwhile, it is known that the resonant tunneling diode, the single electron transistor, the molecular device, and the like can be used to implement a negative differential resistance characteristic with multiple peaks and multiple valleys. However, most of them are difficult to be commercialized due to the stability of logic stages (very small voltage difference between states due to low energy level difference) and limitation on operating temperature (being operable only at a low temperature of 100 K or less due to effects on a thermionic electron emission current).
In regard to a device with NDR characteristics, Korean Patent Laid-open Publication No. 2013-0138045 (entitled “NDR semiconductor device and production process thereof”) discloses an NDR device that can achieve a high PVCR (Peak-to-Valley Current Ratio) with a simple structure in which a transistor is combined with an existing Esaki tunnel diode and has multi-peak current.